During surgery it is very important to observe the patient's level of consciousness and awareness. Few reliable methods of observation exist today. In the field of medical technology there is a problem in producing physical measurements representing the activity in an individual's autonomous nervous system, i.e. in the part of the nervous system, which is beyond the control of the will.
Particularly, there is a special need to establish a state of a sufficiently deep sedation in the patient, in order to avoid administering more anaesthesia than necessary during surgery and general anaesthesia.